1. Field of the Invention
The present invention relates to a plotter which automatically depicts figures, characters etc. on the surface of a sheet or automatically cuts the contours of figures, characters etc. in the surface of a sheet while moving the sheet on a recording surface. More particularly, it relates to improvements in a sheet feed mechanism which moves the sheet, such as a roll of paper, on the recording surface.
2. Description of the Related Art
There has been well known a plotter called the paper moving type wherein, a sheet is placed on a laterally-long recording surface having a vertical section substantially in the shape of a circular arc and in which a pen or the like type of writing utensil or a cutter grasped by a pen carriage is touched down to the surface of the sheet placed on the recording surface. The pen carriage is moved in the lateral direction, namely, X direction of the recording surface on the sheet while the sheet is being moved in the widthwise direction, namely, Y direction of the recording surface on this recording surface, thereby to automatically depict a figure, a character or the like on the sheet surface with the writing utensil or to automatically cut the contours of a figure, a character or the like in the sheet surface with the cutter.
In the plotter, sets of rollers in each of which a drive roller and a pinch roller are opposed to each other are respectively mounted at both the sideward parts of the recording surface so as to be rotatable in the Y direction. Herein, in the state in which both the side edges of the sheet are held between the drive rollers and the corresponding pinch rollers at both the sideward parts of the recording surface, the drive rollers are rotated in the Y direction, thereby to move the sheet in the Y direction on the recording surface.
However, in the case where the sheet is moved in the Y direction on the recording surface in the above way, it wobbles or meanders rightwards and leftwards on the recording surface. Then, the figure, the character or the like depicted on the sheet surface or the contours of the figure, the character or the like cut in the sheet surface become(s) distorted. The appearance of the distortion is conspicuous especially on the occasion that the sheet is a roll of elongated paper and that it is moved in the Y direction on the recording surface over a long distance.
This drawback is ascribable to the fact that the substantial outer diameter of the drive roller mounted at each sideward part of the recording surface is subtly different in the individual places of the peripheral surface of the drive roller, or that either or both the side edges of the sheet held between the drive rollers and the corresponding pinch rollers mounted at both the sideward parts of the recording surface undergoes a slip or the like on the peripheral surface of the drive roller due to any cause.
Incidentally, there has been a plotter wherein, in order to prevent a sheet from wobbling and moving on a recording surface as stated above, small holes are formed at predetermined pitches in both the side edges of the sheet, while sprockets for feeding the sheet are mounted at both the sideward parts of the recording surface so as to be rotatable in a Y direction (the feed direction of the sheet). Herein, the sprockets are rotated in the Y direction while their teeth are being brought into engagement with the small holes in both the side edges of the sheet, whereby the sheet is moved in the Y direction on the recording surface without wobbling.
The plotter, however, can use only the special sheet which is formed with the small holes in both the side edges thereof. Moreover, since the sheet requires a greater width and a stage of work for forming the feeding small holes in both the side edges thereof, it becomes costly to those extents.